2012 Summer Olympics: Time to say goodbye to Michael Phelps, Misty May-Treanor and other retiring greats

America's greatest living poets, Boyz II Men, perhaps said it best: It's so hard to say goodbye to yesterday. But now, as the 2012 Summer Olympics begin to wind down, fans are beginning to face the realization that some of the greatest athletes the world has ever seen have swam their last lap, spiked their last volleyball, and straddled their last pommel horse.

With that in mind, here are five Olympic superstars who you'd better take one good, long, last look at. Because if we take them at their word, when 2016 rolls around they'll be sitting on a porch rocker, reminiscing about the good old days:

Michael Phelps: In case you've been residing under a rock for the past few weeks, yes, Michael Phelps is now the most decorated Olympian in history -- and he's
hanging up his Speedo while he's on top. "I'm retiring. I'm done," he says. "I've been able to go to all these amazing cities in my travels and I haven't been able to see them at all. I see the hotel and I see the pool, that's it. I just want to go and do whatever I want to do. I'm excited."

Misty May-Treanor: Following Wednesday night's (Aug. 8) beach volleyball victory, Misty and her partner
Kerri Walsh Jennings were filled with bittersweet elation -- because although they had just won their third gold medal with a perfect career record of 21 wins and no losses, Misty was standing by her plans to retire. "After London I'm done. A long vacation, finishing baseball season, watching my husband, starting a family," Misty
tells About.com of her future plans alongside her husband, L.A. Dodgers catcher Matt Treanor. "I really enjoy coaching and teaching people who want to learn our sport."

Victoria Pendleton: Like Phelps, this British cyclist is choosing to quit at the height of her athletic ability, determined to go out on top. A nine-time world title winner, Pendleton won the gold in this summer's Keirin race and the silver in the sprint event. "Over the last 10 years it's been a hectic, rollercoaster ride for me. It's just been one event after the other, going to the next World Championships, do that, do this," she
tells the Manchester Evening News. "I'm looking forward to having a bit more time to think, savoring the moment and enjoying it for what it is and looking back and hopefully feeling very proud of what I've achieved."

Wu Minxia: One of the best female divers in history, China's Wu Minxia recently announced her plans to retire, just around the same time as she was securing her sixth Olympic medal. "I think this is the perfect ending for me," she
tells the UK's Daily Mail. "I'm very happy to have this ending."

Shawn Johnson: A bit different than the others listed above, Johnson wasn't even able to compete in the 2012 Olympics because of the knee injury that will ultimately end her career. But that doesn't change the fact that the U.S. gymnast is a four-time medalist, and will always be a legend thanks to the 2008 Olympics. Although she's only 20 years old, Johnson announced her retirement this past June, and gymnastics fans undoubtedly miss her presence in this and future Olympics.

Which athletes will you miss if they don't return for the 2016 Olympics?